1. Field of the Invention
The present invention relates to a magnetic resonance imaging (MRI) apparatus which utilizes a magnetic resonance phenomenon to generate a magnetic resonance image and an image generation method in the MRI apparatus.
2. Description of the Related Art
A magnetic resonance imaging apparatus is one which visualizes chemical and physical micro information of a substance or observes a chemical shift spectrum by utilizing the phenomenon in which a group of nuclei resonantly absorbs energy of a radio frequency magnetic field rotated at a specific frequency when the group of nuclei having intrinsic magnetic moments is placed in a uniform static magnetic field.
For example, a diagnostic image is taken by the magnetic resonance imaging apparatus as follows: A patient is placed in a combined magnetic field including a static magnetic field formed by a magnet and a gradient magnetic field formed by a gradient magnetic field coil. A radio frequency wave having a predetermined frequency is applied to the patient set in the above-described situation in order to generate the magnetic resonance phenomenon. A magnetic resonance signal is generated by the applied radio frequency wave in the patient, and the magnetic resonance signal is received with a reception radio frequency coil to form the image.
In such an MRI apparatus, U.S. Pat. No. 5,928,148 (hereinafter referred to as First Reference) and U.S. Pat. No. 5,808,468 (hereinafter referred to as Second Reference) are well known as a technology which enlarges an imaging range.
In the MRI apparatus disclosed in First Reference, vertically divided coils are previously fixed to an imaging region in a gantry, and the image can be obtained in a wide region while a patient is moved between the vertically divided coils.
In the MRI apparatus disclosed in Second Reference, a table for holding a coil is placed on an already-existing couch as means for vertically fixing coils. A second movable couch is placed on the table, and the patient loaded on the second couch is conveyed into the gantry in a sliding manner.
However, in the technologies disclosed in First Reference and Second Reference, since the coil is fixed, a distance between the coil and the patient is increased, and sensitivity can not be efficiently increased.
An MRI apparatus including a whole body radio frequency coil and a movable surface coil is disclosed in Jpn. Pat. Appln KOKAI Publication No. 64-37939 (hereinafter referred to as Third Reference).
However, in the technology disclosed in Third Reference, because the imaging is performed after the surface coil is brought close to the imaging region, the imaging range in one time becomes narrow.